The main objective of the proposed research is to elucidate how the mammalian central nervous system regulates body temperature. The regulator resides in the pre-optic nuclei and the hypothalamus and its main feedback loops are hypothalamic temperature, cutaneous temperature, and spinal temperature. Using chronically implanted, water-perfused thermodes and ambient temperature control, we manipulate these feedback parameters and measure the output of the regulator by quantifying thermoregulatory responses, using primarily techniques of direct and indirect calorimetry, hygrometry, and precision thermometry. Thereby, we can describe the characteristics of the controlled and controlling systems and can then study the influences of other variables such as hibernation, sleep, exercise, pyrogens, and prostaglandins on the characteristics of the regulator. The working hypothesis for the proposed research is a simple, general, neuronal model of this regulatory system which is compatible with existing data. The experiments proposed are designed to test, refine, and extend that model. The specific aims of the proposed research are: (1) to measure the alterations in the characteristics of the regulator as animals go through the stages of sleep, torpor, and deep hibernation; (2) to correlate cortical EEG and electrical activity in specific brain structures with thermoregulatory events during the hibernation cycle; (3) to compare quantitatively the influences of peripheral, POH, and spinal thermosensitivity on the regulators of mammals of various body sizes; (4) to investigate the mechanisms of prostaglandin-induced fever; and (5) to make a comparative study of the avian thermoregulatory system and establish a simple neuronal model describing it.